JPH01202394A - Solid wire for gas shielded arc welding of galvanized steel and its welding method - Google Patents

Abstract

PURPOSE:To obtain a sound weld metal part difficult to generate pit and blowhole by specifying the composition of a solid wire. CONSTITUTION:The composition of the solid wire for gas shielded arc welding of a galvanized steel sheet contains 0.02-0.20% C, 0.10-0.70% Si, 0.20-2.0% Mn, 13-80% Ni, <=0.02% P, <=0.02% S and <=0.040% N in wt.% and the balance Fe with inevitable impurities. A sound welding metal without any pit generation and with extremely less blowholes can thus be obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a solid wire and a welding method used in gas-shielded arc welding. The present invention relates to a solid wire for gas-shielded arc welding of galvanized steel sheets and a gas-shielded arc welding method that can provide a sound welded metal part that is unlikely to generate blowholes or blowholes.

[Prior Art] Examples of steel materials that have been subjected to antirust treatment and have excellent corrosion resistance include galvanized steel sheets. Galvanized steel sheets are ordinary hot-rolled or cold-rolled steel surfaces coated with galvanized steel, and their main uses include roofing sheets and other building materials, gasoline cans, washing machine parts, and other materials. In recent years, there has been a trend toward its use in surface-treated steel sheets for automobile bodies.

When welding galvanized steel, zinc, which has a boiling point lower than the melting point of iron (906°C), enters the melt during welding and bumps the zinc vapor, which does not float up during the weld metal solidification process and remains as bubbles, causing pits and blowholes. Frequent defects such as

These defects result in a cross-sectional loss of the required weld metal, which is undesirable from the viewpoint of ensuring the strength of the structure, and furthermore, the pits reduce the commercial value in terms of appearance.

In thin plate welding, the welding speed is high and the welding heat input is small, and the joint shape is easily affected by the steel plate surface, such as overlaps and fillets, so defects are likely to occur.

Measures to reduce the harm caused by zinc include: ■ Mechanically removing zinc from the weld line in advance; ■ Incineration of zinc with a preliminary heat source; ■ Adopting a welding method that is insensitive to zinc; ■ Possible Measures have been taken to select welding conditions that are less likely to cause defects, but none of these are essential countermeasures.

For example, manual welding is a method that is less likely to cause pits and blowholes, and hand welding rods such as illuminite and titania are particularly effective. However, this welding method has a slow welding speed and a large heat input, so it is not suitable for welding thin plates because it causes significant welding distortion.

However, gas shield welding using solid wire, which is the most commonly applied method for welding thin plates, is relatively susceptible to the effects of zinc.

As a technology for preventing defects such as pits and blowholes on surface-treated steel sheets, JP-A-59-45096 discloses a technique for preventing pits and blowholes on surface-treated steel sheets, targeting primer coated steel sheets containing zinc powder.
Welding materials containing e, Sb, and S as appropriate have been proposed. However, a welding material having such a composition cannot be expected to be effective in welding galvanized steel sheets, which is the object of the present invention.

[Problems to be Solved by the Invention] The present invention provides a solid wire for gas-shielded arc welding and a welding method that solves the occurrence of defects such as pits and blowholes that occur in gas-shielded welding of galvanized steel sheets as described above. It is something.

[Means to solve the problem] In the present invention, C: 0.02 to 0.20k in weight%.

Si: 0.10-0.70% F, Mn: 0
．． 20-2.0% F, Ni: 13-80 zero, P: 0.02 or less, S: 0.02%i or less, N: 0.040 or less, and the remainder is F.
The solid wire for gas-shielded arc welding is characterized by comprising e and unavoidable impurities, and further contains 5 to 30 Vouk of CO2 or 2 to 30 Vouk in this wire and Ar.
By using a shielding gas mixed with 02 of 1OVd zero, droplets are not transferred to the base metal side during the peak current, which is the high current range of the pulsed DC current with the wire as the positive electrode, and the melt is melted during the low base current. A method for pulsed arc welding of galvanized steel sheets, which is characterized by welding while performing droplet transfer.

[Function] As mentioned above, the present inventors found that pits and blowholes are likely to occur in galvanized steel sheets in particular in gas shield welding using solid wires due to (a) low boiling point that enters the molten weld metal. Zinc at (906°C) turns into vapor and forms bubbles.

(0) This is thought to be due to the fact that solid wire gas shield welding, which does not use coating or flux, has a fast solidification rate, and the zinc vapor that has become bubbles in the weld metal tends to remain in the weld metal without being able to float to the surface, which is especially noticeable during high-speed welding. Ta.

To reduce this effect of zinc, (a) make it difficult for zinc vapor to remain in the weld metal as bubbles; (b)
Based on the viewpoint that it is effective to suppress the amount of zinc that penetrates into the weld metal, the present invention was constructed by conducting studies from both the wire composition and the welding method.

First, the wire of the present invention will be described below.

In order to reduce the number of bubbles remaining in the weld metal, we believe that the most effective means are - Making the weld metal have a low melting point and increasing the bubble floating time - Alloying and fixing zinc, etc. We considered the effects of various elements to be effective. As a result, we found that Ni is an element that satisfies these requirements.

Figure 1 shows the influence of Ni on the brohol generation rate, and shows the effect of Ni on the brohol generation rate. : Corresponding St-Mn system (target component C: O, 0B96.S
i: 0.8%, Mn: 1, Tsume, P: 0.0296. S:
0゜02JN: Wire (diameter: 1
．． 2 mmφ), and test plates of the steel type and zinc coating amount shown in Table 1 (plate pressure t = 2.3 mm).

Width W = 50 mm, length 11 = 300 mm) were stacked as shown in Fig. 2, stacked downward in the fillet position, and the shielding gas was Ar”20k (:02 (flow rate: 20ff).
i/min), gas shield welding was performed under the welding conditions shown in Table 2, and the blowholes generated in the fillet bead were measured and compared.

Table 1 Steel type and zinc deposit Table 2 Welding conditions To measure the blowhole, perform a radiographic test on each bead obtained, and measure the blowhole width in the bead length direction using a 10x magnifying glass. Then, the occurrence rate (96) was determined from the sum of the blowhole widths relative to the bead lengths.

The effect on brohols is relatively small in the range of 0 to less than 10 zeros, but in the range of about 10 zeros or more, the brohol generation rate decreases significantly and stably. The reason for this is that Ni
This is thought to be because as the amount increased, the melting point of the weld metal decreased and the time until solidification became longer, promoting the floating of air bubbles. In addition, the analysis results of zinc in the weld metal of samples taken from locations where blowholes have not occurred show that N
An increase in the amount of zinc was observed as t increased. This result shows that Ni forms an alloy with zinc and fixes the zinc.
This supports the above-mentioned concept of reducing the harmful effects of zinc.

In order to further enhance the effects of Ni and ensure welding workability, bead shape, etc., it is necessary to limit the ranges of C, Si, and Mn, as well as P, S, and N. The reasons for limiting each element will be described below.

C has the effect of suppressing the generation of broholes, and this effect is 0.02! It is effective when adding li or more, but 0
．． If it exceeds 2H, the risk of bead hardening and hot cracking increases significantly, so the upper limit was set as a,'io''<.

St of gas shield welding wire is usually added in sufficient amount as an important deoxidizing element. However, since the wire of the present invention has poor blowhole properties,
Additions as low as possible are preferred. The optimum amount to be added depends somewhat on the mixing ratio of carbon dioxide or oxygen in the shielding gas, but as long as St is 0.70%i or less, good blowhole resistance can be obtained in any shielding gas composition. . But 0.10! If the groove is not grooved, bits and blowholes will rapidly increase due to insufficient deoxidation, and problems such as a convex bead shape will occur.

The range of St depending on the shielding gas composition is, for example, 0.30 to 0.70 in the case of CO2! To, Ar to 5-201
0 when adding CO2 or 2~10960z
．． A range of 10 to 0.40 is preferable.

The reason why the appropriate value exists in a lower range is that by making the deoxidation somewhat insufficient, the release of oxygen in the weld metal becomes active, which promotes the floating of zinc bubbles. Conceivable.

Mn shows the same tendency as St in the case of pore generation due to zinc, but since the degree of influence is small, addition over a wide range can be tolerated. But 0.20! When Si is less than li, many pores occur due to insufficient deoxidation even when Si is at the upper limit. 2. In Ocho, the bead hardens significantly, so
2.0! Ii was set as the upper limit.

As mentioned above, when Ni is added in an amount of about 11 or more, the pore resistance is significantly improved, but stable effects can only be obtained with Ni in amounts of 13 or more.
It is greater than or equal to zero. This effect is maintained up to about 90 zero, but considering economic efficiency, the upper limit was set to 80 zero.

P and S are elements that inhibit cracking resistance, and it is preferable to suppress them as much as possible, especially in the wire of the present invention in which Ni is added, but the purpose is achieved if both are 0.02X or less.

If N exceeds 0.04, the generation of pores becomes significant, so it is limited to 0.04096 or less. The wire of the present invention can be made by rolling and drawing a steel ingot in the same way as ordinary wire.
It can be manufactured with copper plating if necessary.

Even when welding a galvanized steel plate using a wire with the above-mentioned composition and using a shielding gas containing CO2 or 8R mixed with CO2, there will be no bits, and there will be very few blowholes, resulting in a structurally It is quite satisfactory for practical use.

Next, the effects of the wire of the present invention can be more effectively achieved by a welding method that suppresses the amount of zinc penetrating the weld metal as much as possible.

Figures 3 and 4 show the arc state and welding transition state according to the pulse arc welding method for galvanized steel sheets of the present invention. 1 is the welding torch of the DC power source, 2 is the solid wire of the positive electrode (+), 3 is the arc column at peak current, and 4 is the base generated by the arc from the tip of the solid wire. 5 is the weld metal, 6 is the shielding gas, 7 is the zinc layer plated on the surface of the base material, and 8 is the base material connected to the negative electrode (-).

In the present invention, periodically repeating pulsed DC current is applied to a large current arc at peak current as shown in Fig. 3, and the zinc plated on the surface of the base material near the arc is irradiated and melted and evaporated. As shown in the figure, a cycle in which welding is short-circuited from the tip of the solid wire to the base metal side during base current is performed for each pulse current cycle.

This method reduces the harmful effects on arc welding caused by zinc combustion gas and vapor penetrating into the weld metal, stabilizes the arc, and reduces defects such as blowholes inherent in the weld metal and bits that occur on the surface of the weld metal. Furthermore, the amount of spatter generated is small, and beautiful weld metal can always be formed.

In addition, when using a wire with a diameter of 1 or 2 mm, the appropriate current value for this effect is 400 A or more at the peak current and 100 A or less for the base current, so that the droplet 4 can smoothly short-circuit to the base material at the base current. To make the transition, use a mixture of 5~30VoL! and 0Co2 or 2~1ovO exchange%0□ as the shield gas 6.
The appropriate pulse frequency is in the range of 150 to 300 Hz.

In welding galvanized steel sheets using the pulse arc welding method of the present invention configured as described above, a healthy and beautiful weld bead can be obtained.

The effects of the present invention will be specifically explained below using Examples.

[Example 1] Wire with chemical composition shown in Table 3 (diameter = 1.2 mmφ)
Welding was carried out in the same manner as in the above-mentioned case in which the results shown in FIG. 1 were obtained, and the resulting bead was examined for bits and blowhole formation, and the results shown in Table 3 were obtained. The number of pits generated is determined by counting the number of bits on the weld bead surface and calculating the number of pits generated per 1 m welding length from the weld bead length (
The evaluation was carried out in terms of number of particles/m). Further, as shown in Table 3, the shielding gas composition is set for each wire, and the welding voltage is also selected at a value suitable for the shielding gas composition.

In Table 3, wires N011 to N009 are comparative example N
o, 10 to No. 18 Wires according to embodiments of the present invention are shown.

All of the wires No. 011 to 9 have a Ni content of 13! Because it is less than ¥, pits and blowholes occur frequently.

In particular, C[No, 3], St [No, 4], N[
No, 5. No. 7° No. 8] of each wire exceeds the limited range, the blowhole generation rate is also high.

On the other hand, in the wires of the present invention No. 10 to No. 18, no bits were generated, the blowhole generation rate was very low, and sound weld metal was obtained.

[Example 2] No. 1 in Table 3. No, 14. Galvanized steel plates were welded using wire No. 17 in the same manner as in Example 1. Table 4 shows the test conditions such as the type of power source, current, voltage, and shielding gas composition, and the results obtained. The conditions for pulsed arc welding are: pulse peak current: 450A, base current: 50^, pulse frequency:
The frequency was set to 240Hz.

In addition, the amount of spatter was measured using a copper collection box (2, Qmm).
The collected spatter was weighed at tX 200wX L5Qhx 3QOmm, and the generation amount (g/m1n) was determined from the average value of each three weighing values, welding arc, and time.

Test No. 1-=No, 6 is a comparative example, Test No. 7-N
0 and 13 show examples of the welding method of the present invention. Exam No.
1, No. 2, and No. 2 are conventional wires (No. 1) and DC power supplies. When the shielding gas is CO2 (NO. 1), bits and blowholes occur frequently, and the amount of spatter is also extremely large. Ar+20
Even with '4COz (No, 2), although the amount of spatter generated is slightly reduced, the porosity resistance is not improved. Test No. 3. No. 4 is the conventional wire (No. 1) that has been subjected to arc pulse arc welding using a pulse power source, and although the amount of pits, blowholes, and spatter generated tends to decrease compared to when using a DC power source, all are satisfied. It has not reached the level. Test No.5. No. 6 is the wire of the present invention (No.

This is an example in which pulsed arc welding was performed in step 14), but since the shielding gas composition was outside the limited range of the present invention, both the bit, blowhole, and spatter amount were compared to test No. 1 using conventional wire.
, not much different from the case of 3.4.

On the other hand, in the case of the present invention of Test No. 67 to No. 13,
No pits were observed, the blowhole rate was extremely low, and the amount of spatter was reduced to the same level as with ordinary steel sheets.

[Effects of the Invention] As described above, according to the wire and welding method of the present invention,
Even when welding anti-corrosion treated steel materials such as galvanized steel sheets, a healthy weld metal with very few blowholes and no bits is generated, which increases the strength of the structure without causing cross-sectional defects in the weld metal. Do not deteriorate. Furthermore, since no pits are generated, a weld bead that is pleasing in appearance can be obtained.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between Ni content and blowhole generation (double positive), Figure 2 is a perspective view showing the shape of the test plate, and Figure 3 is the arc state at peak current in pulsed arc welding of galvanized steel sheets. FIG. 4 is a schematic diagram showing the droplet transfer state. Like FIG. 3, it is a schematic diagram showing the arc state and the droplet transfer state at the base current. 1... Welding torch of DC power source 2... Solid wire 3... Arc column at peak current 4... Droplet 5... Weld metal 6... Shielding gas 7... Galvanized layer 8...Base material
W-...Welding direction Fig. 1 Ni (%)

Claims (1)

[Claims] 1% by weight, C: 0.02-0.20%, Si: 0.
10-0.70%, Mn: 0.20-2.0%, Ni:
13-80%, P: 0.02% or less, S: 0.0
2% or less, N: limited to 0.040% or less, the remainder being F
A solid wire for gas-shielded arc welding of galvanized steel sheets, characterized by comprising e.g. and inevitable impurities. 2. The wire according to claim 1 and 5 to 30 Vol in Ar.
Using a shielding gas mixed with % CO_2 or 2 to 10 Vol% O_2, droplets are not transferred to the base metal side at the peak current of the pulsed DC current using the wire as the positive electrode,
A gas-shielded arc welding method for galvanized steel sheets, which is characterized by welding while performing droplet transfer during base current.